Characterization of random-sequence proteins displayed on the surface of Escherichia coli RNase HI

In a previous study, random-sequence proteins of 120-130 amino acid residues mere inserted into the surface loop region of the enzyme, Escherichia coli RNase HI [Doi et al, (1997) FEBS Lett, 402, 177-180], Here we established that the RNase H activity of the insertion mutants is correlated with their secondary structure contents evaluated by circular dichroism measurement at 222 nm, The random-sequence insert of a mutant enzyme possessing relatively high RNase H activity was detached from the RNase HI scaffold, and its characterization indicated that the random-sequence protein maintains its secondary structure after separation from the scaffold. Thus, the structural features of random-sequence proteins were suggested to be monitored by measuring the activity of the scaffold enzyme into which these proteins have been inserted, (C) 1998 Federation of European Biochemical Societies.